Seismic performance and strain localization in a historic masonry minaret: A comparative evaluation of internal steel strengthening strategies

Abstract

In this study, the seismic performance of a historic masonry minaret was investigated through nonlinear time-history analyses, and the relationship between global stiffness enhancement and local strain localization was evaluated. Four different internal steel strengthening scenarios, developed within a finite element model constructed by jointly considering experimental studies conducted on similar stone specimens and parameter ranges proposed in the literature, were comparatively analyzed under three distinct ground motion records. The modal analysis results indicated that the natural frequencies increased significantly in all strengthening scenarios, demonstrating a substantial improvement in overall structural stiffness. However, nonlinear dynamic analyses revealed that an increase in stiffness does not necessarily lead to an improvement in seismic performance. Displacement–time histories showed that the onset of instability was delayed in certain strengthening configurations; nevertheless, none of the interventions was able to completely prevent global collapse. The maximum principal strain distributions demonstrated that the collapse behavior was governed by tensile-dominated strain localization developing at the shaft–substructure transition region. In particular, strengthening configurations exhibiting partial continuity were found to induce stiffness discontinuities that could trigger early instability. The results indicate that the seismic performance of masonry minarets is closely related not only to global stiffness enhancement but also to the tensile strength, damage-softening characteristics, and energy dissipation capacity of the material. The study provides significant implications for performance-based strengthening design of masonry structures with cultural heritage value.